Nan Madol — not technically underwater but half of it is sinking and the underwater part is unexcavated

okay Nan Madol is technically above water. mostly. it's the artificial island complex off Pohnpei in Micronesia, built from basalt logs stacked like Lincoln logs. 92 artificial islets, connected by canals, covering 18 square km. but here's the part that doesn't get covered: the seaward sections are……